1. Field of the Invention
The invention relates to a brake stroke sensor. In particular, the invention relates to a digital brake stroke sensor for determining a position of a pushrod used in an airbrake chamber.
2. Discussion of Background Information
Commercial vehicles typically use air-powered brake systems. Forcing compressed air into a brake actuator chamber pushes a pushrod out of a brake actuator service chamber. The emerging pushrod operates an S cam or disk brake mechanism, which forces the brake shoes/pads against the drums/rotors.
Over time, the brake shoes or pads associated with an individual wheel will begin to wear. The pushrod must accordingly travel a greater distance in order to force the brake shoes or pads against the drums or rotors to provide appropriate braking friction. Because the pushrods have a limited length of travel, the brake shoes or pads can wear down to the point that a fully extended pushrod no longer provides adequate pressure to exert sufficient braking force. Many agencies enforcing federal and state vehicle regulations therefore utilize the length of pushrod travel as a measure of whether the brakes are functioning properly.
It is desirable to maintain and monitor the proper functioning of a vehicle""s brake system to enhance the safety of the driver and to the general public, and to help determine whether it meets federal safety standards for correct operation. If the braking system of a commercial vehicle does not meet federal operational requirements, the commercial vehicle can be placed out-of-service until the problematic components are repaired and returned to acceptable operational limits.
Electronic parametric monitoring devices that warn of an out-of-tolerance condition have not been widely used and have not been generally installed by original equipment manufacturers on new commercial vehicles. After market electronic systems tend to be generally lacking, expensive, not readily compatible with various types of vehicles, and difficult to install. In addition, these systems do not relay the actual pushrod stroke to the vehicle operator.
According to an embodiment of the invention, a brake stroke sensor for determining a position of a brake chamber actuator pushrod is provided. At least two sequences of magnets are configured to move in association with the pushrod. The at least two sequences of magnets collectively form a Grey code. A sensor system is configured to detect a polarity of the magnets at positions adjacent to the sensor system and produce at least one signal indicative of the polarity. A processor is configured to convert the at least one signal into an indication of the position of the pushrod.
The above embodiment may have various optional features. By way of non-limiting example, a first of the at least two sequences of magnets can be shifted relative to a second of the at least two sequences of magnets. The sensor system an include a sensor for each sequence of the at least two sequences of magnets. A first sensor of the sensor system can be shifted relative to a second sensor of the sensor system. Each sensor can be a Hall-Effect switch. The at least two columns can be seven columns. The at least two sequences of magnets can be out of electrical contact with the sensor system. The at least two sequences of magnets can be enclosed within a non-conductive covering. The at least two sequences of magnets can be disposed about the pushrod at substantially equidistant positions.
According to another embodiment of the invention, a brake stroke sensor for detecting a position of a brake pushrod is provided. A plurality of columns of magnets are configured to move in accordance with the pushrod, at least one of the plurality of columns of magnets being shifted along its axis relative to another column of magnets. A sensor for each column of magnets the sensor being configured to detect a pole of a magnet in the column of magnets within a sensing range of the sensor. A processor is configured to receive data originating from each sensor and to provide an indication of a position of the brake pushrod.
The above embodiment may have various optional features. By way of non-limiting example, the plurality of columns of magnets can extend axially along the pushrod and collectively define a plurality of rings of magnets radially along the pushrod, such that the plurality of rings of magnets collectively form a Grey code. A non-conductive sheath can enclose the plurality of columns of magnets. The plurality of columns of magnets can be disposed about the pushrod at substantially equidistant positions. The sensors can be Hall-effect switches.
According to yet another embodiment of the invention, a method of determining a position of a brake actuator pushrod is provided. The method includes configuring a plurality of columns of magnets to move in accordance with the brake actuator pushrod, at least one column of magnets being shifted in a direction parallel to the brake actuator pushrod relative to another column of magnets, monitoring, as the pushrod moves relative to a location, a polarity of each of the plurality of columns of magnets adjacent the location, converting the results of the monitoring into an indicator signal representing the position of the brake actuator pushrod, and outputting, in accordance with the indicator signal, data that indicates the position of the brake actuator pushrod.
The above embodiment may have various optional features. By way of non-limiting example, at most one of the detected slates of the plurality of magnets changes at a time. The configuring can include configuring the plurality of columns of magnets to define a Grey code. The monitoring can include providing Hall-effect switches.
According to yet another embodiment of the invention, a method of detecting a relative position of a brake pushrod is provided. The method includes configuring a plurality of magnets to move in accordance with the pushrod, where the plurality of magnets collectively form a Grey code, arranging a sensor system at a location, sensing, by the sensor system, a plurality of magnet poles from the plurality of magnets adjacent the location, and producing, from the results of the sensing, a positional signal being representative of the relative position of the brake pushrod.
The above embodiment may include various optional features. By way of non-limiting example, at most one of the detected states of the plurality of magnets changes at a time. The configuring may include configuring the plurality of columns of magnets to define a Grey code. The sensing may include sensing using Hall-Effect switches.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawings.